1. Field of the Invention
This invention relates to polylactic acid based resin molded articles which comprise polylactic acid which is a biodegradable resin.
2. Related Art
Synthetic resins which use petroleum as the material are broadly used, because they have excellent performance such as their light weight, corrosion resistance and easy molding, as well as their low costs. However, since their degradability under the natural environment is low and their exothermic power at the time of incineration is large, it is necessary to reconsider about the use of the aforementioned synthetic resins from the viewpoint of environmental protection. Under such circumstances, biodegradable resins have been drawing attention in recent years, because they are biodegraded after their use by the action of microorganisms, namely, the molecules once incorporated by microorganisms are converted into water, carbon dioxide and the like and discharged as a result of the metabolism carried out by the microorganisms.
Though there are various kinds of biodegradable resins, aliphatic polyesters as biodegradable resins of chemical synthesis system, particularly polylactic acid (PLA) as a non-petroleum system circulation type plant resin which uses lactic acid obtained by fermenting corn, sugar cane or the like as the material, are particularly expected because of the superior performance and low cost. However, polylactic acid is unsuitable for applications which require heat resistance, because it has low heat resistance and is apt to change the shape by undergoing influence of heat.
On the other hand, a technique so-called polymer blend or polymer alloy is conventionally known as one of the methods for improving physical properties of resins. According to this technique, a different species of resin is mixed and kneaded with another resin which becomes the object of the physical property improvement. Attempts have also been made to improve heat resistance of polylactic acid using this technique. For example, JP-A-2005-307128 discloses a polylactic acid based resin composition in which a crystalline polypropylene system resin composition comprising a modified polypropylene resin and inorganic filler are mixed with polylactic acid. The modified polypropylene resin is a product obtained by carrying out graft modification of a crystalline modified polypropylene system resin with an ethylenic unsaturated bond-containing carboxylic acid or an anhydride or derivative thereof.
However, by the polylactic acid based resin composition described in JP-A-2005-307128, in which a crystalline polypropylene system resin composition and inorganic filler are mixed with polylactic acid, heat resistance of polylactic acid can be improved, but on the contrary, its Young's modulus in flexure is increased due to its hardening. Accordingly, there is a problem in that this polylactic acid based resin composition cannot be applied to resin molded articles which also require flexibility in addition to heat resistance.